Discharge lamp igniting and operating circuit with a timer controlled output voltage limit

Abstract

The invention relates to a circuit arrangement for igniting and operating a high-pressure discharge lamp provided with a control circuit which limits the voltage to a value Vb across the output terminals of the circuit arrangement such that: Vla<Vb<Vi. wherein Vla is the nominal lamp voltage and Vi is the threshold voltage across the output terminals at which the ignitor starts.

We claim: 
     
       1. A circuit arrangement for igniting and operating a high-pressure discharge lamp, comprising: input terminals for connection to a supply source,   output terminals for connection to the lamp,   switching means for operating the lamp at a nominal lamp voltage Vla during stable lamp operation and for generating an open voltage Vo at the output terminals before the lamp has ignited,   ignition means responsive to the voltage at the output terminals for generating an ignition voltage pulse when the voltage at the output terminals reaches a threshold value Vi, and   a control circuit for controlling the switching means, characterized in that the control circuit includes means for limiting the voltage at the output terminals to a level Vb such that   Vla<Vb<Vi.       
     
     
       2. The circuit arrangement of claim 1, wherein the control circuit includes a timer for establishing a prefixed period of time after which the voltage at the output terminals is at the level V b . 
     
     
       3. The circuit arrangement of claim 2, wherein the control circuit further includes a voltage buffer network coupled to the timer to shield the timer from transient conditions occurring in the supply source. 
     
     
       4. The circuit arrangement of claim 3, wherein the control circuit is responsive to the voltage across the output terminals and current flowing through the lamp. 
     
     
       5. The circuit arrangement of claim 4, wherein the prefixed period of time is set to provide hot reignition of the lamp. 
     
     
       6. The circuit arrangement of claim 1, wherein the control circuit is responsive to the voltage across the output terminals and current flowing through the lamp. 
     
     
       7. The circuit arrangement of claim 2, wherein the prefixed period of time is set to provide hot reignition of the lamp. 
     
     
       8. The circuit arrangement of claim 2, wherein the timer includes a reset which is enabled upon application of a supply voltage thereto.